1. Field of the Invention
The present invention generally relates to a portable GPS type distance/speed measuring apparatus. More specifically, the present invention is directed to a portable type distance/speed meter capable of calculating/displaying both a travel distance and a travel speed based upon positioning data acquired by receiving GPS electromagnetic waves, while being mounted on an arm of a user, like a wrist watch.
2. Description of the Related Art
In the GPS (Global Positioning System), 24 sets of the GPS satellites orbit on 6 sets of orbit courses located at an inclined angle of 55 degrees at a distance of approximately 20,200 km on the earth, and travel for approximately 12 hours per one turn. While navigation data required for positioning, transmitted from more than 3 GPS satellites under the most receivable condition are received by a GPS receiver, positioning calculations are carried out by measuring propagation delay time of these navigation data so as to determine travel direction/present position of a user.
In this GPS, two different frequencies "L1 (=1.57542 GHz)"and "L2 (=1.22760 GHz)" are prepared for the transmission frequencies of the GPS satellites. Since the C/A code (namely commercial-purpose code being free-opened) is transmitted at the frequency of 1.57542 GHz (equal to GPS transmission frequency "L1"), one GPS transmission frequency "L1" is utilized in general-purpose positioning operation. It should be understood that the GPS signal having this frequency "L1" is modulated in the PSK (Phase Shift Keying) modulating method by using the pseudonoise code, and then the PSK-modulated GPS signal is transmitted by way of the spread spectrum communication system. This pseudonoise code corresponds to the synthesized wave made from the C/A code used to discriminate the desirable GPS satellite from all of the GPS satellites, and also the navigation data such as the GPS satellite orbit, the GPS satellite orbit information, and the time information.
FIG. 5 is a schematic block diagram representing an arrangement of a GPS receiver 200 capable of receiving a GPS electromagnetic wave (namely, GPS signal having frequency of "L1 (=1.57542 GHz)") transmitted from a GPS satellite. As shown in FIG. 5, the GPS receiver 200 is arranged by a reception antenna 201, an L-band amplifying circuit 202, a down-converter circuit 203, a voltage comparing circuit 204, a message decrypting circuit 205, and a positioning calculating circuit 206. The reception antenna 201 receives GPS electromagnetic waves transmitted from the GPS satellites. The L-band amplifying circuit 202 amplifies a GPS signal having an L-band frequency among the received GPS signals. The down-converter circuit 203 performs a down-converting operation of the amplified GPS signal by multiplying this received GPS signal by a signal produced from a local oscillating circuit 107. The voltage comparing circuit 204 digitally converts the GPS signal down-converted by the down-converter circuit 203 into a digital GPS signal. In the message decrypting circuit 205, the digital GPS signal inputted from the voltage comparing circuit 204 is multiplied by a C/A code generated from a C/A code generating circuit 208 so as to acquire both navigation data and carrier wave phase information corresponding to a pseudodistance. The positioning calculating circuit 206 calculates positioning data by using both the navigation data and the carrier wave phase information, which are entered from the message decrypting circuit 205. It should also be noted that the local oscillating circuit 107 corresponds to such a circuit capable of producing a signal used to convert a received GPS signal into another signal having a desirable frequency.
Next, reception operation of this GPS receiver 200 will now be described. In FIG. 5, the L-band amplifying circuit 202 selectively first amplifies the GPS signal having the frequency of 1.57542 GHz received by the reception antenna 201. The GPS signal amplified in the L-band amplifying circuit 202 is entered into the down-converter circuit 203. This down-converter circuit 203 converts this entered GPS signal into a first IF (intermediate frequency) signal having a frequency of from several tens of MHz to 200 MHz by using the local oscillation signal produced from the local oscillating circuit 107, and furthermore, converts this first IF signal into a second IF signal having a frequency on the order of from 2 MHz to 5 MHz. Then, the voltage comparing circuit 204 enters thereinto this second IF signal so as to digitally convert the second IF signal into the digital GPS signal by employing a clock signal having a frequency several times higher than the frequency of this entered second IF signal. In this circuit, this digitally-converted GPS signal will constitute spectrum-spread data (digital signal).
This spectrum-spread data outputted from the voltage comparing circuit 204 is entered into the message decrypting circuit 205. Then, this message decrypting circuit 205 reverse-spreads the C/A code produced from the C/A code generating circuit 208 to the entered digital signal so as to acquire both the navigation data and the carrier wave phase information corresponding to the pseudodistance. The C/A code implies the pseudonoise code identical to that of the GPS satellite.
The above-explained reception operation is carried out with respect to the respective GPS satellites in this GPS receiver 200. Normally, the message decrypting circuit 205 of the GPS receiver 200 may acquire the navigation data and also the carrier wave phase information of 4 sets of the GPS satellites, and then the positioning calculating circuit 206 acquires the positioning data (speed, present position, time information etc.) based upon the acquired navigation data/carrier wave phase information. The positioning data acquired by the positioning calculating circuit 206 is outputted to a CPU (not shown) for controlling the overall reception operation of this GPS receiver 200, or externally outputted as a digital signal. Such a GPS receiver is utilized as a car navigation system by combining positional information of GPS with map information produced from a CD-ROM.
On the other hand, the above-explained GPS receiver 200 is realized in the form of such a portable type GPS receiving apparatus capable of measuring travel speeds/travel distances of persons, since the GPS receiver 200 may be supplied as a digital ASIC (Application Specific IC) due to current technical progresses in semiconductor fields. This portable type GPS receiving apparatus calculates the travel distance and the travel speed of the user based upon the positioning data acquired by employing the GPS receiver 200, and then displays both the travel distance and the travel speed.
Furthermore, since such a portable type GPS receiving apparatus is made compact and in light weight, this portable type GPS receiving apparatus may be mounted on an arm of a user like a wrist watch. It is proposed that this idea is very useful especially in the case that a marathon runner wants to measure both a running speed and a running distance. When such a portable type GPS receiving apparatus is mounted on the arm of the user, the GPS receiver mounted on this portable type GPS receiving apparatus normally calculates the measurement results as the travel speed and the travel distance of the user. The measurement results are constituted by superimposing the positional change of the entire user body on the positional change caused by the arm swinging action.
In this case, since the information which is desirably acquired by the user corresponds to both a travel speed and a travel distance calculated based on motion of the entire user body (will be referred to as "true motion" hereinafter), an error may be produced, which is adversely caused by the positional change by the arm swinging action. As a consequence, in the conventional portable type GPS receiving apparatus, an attention is paid that the arm swinging action is periodically changed along the forward/backward directions with respect to either the walking direction or the running direction, so that the adverse influence caused by the arm swinging action may be reduced by calculating the average value of the travel speeds acquired from the GPS receiver within a predetermined period.
However, as to the normal GPS receiving process operation executed in the GPS receiver, the GPS electromagnetic waves are received in a predetermined sampling period (for instance, 1-second interval), and then the positioning data is acquired from the received GPS electromagnetic waves. All of the positioning data about all of the positions cannot be acquired, which are periodically changed by the arm swinging action of the user. Therefore, even when the above-explained travel speeds are averaged, the travel speed originated from the true motion cannot be always calculated.
FIG. 6 is a graph representing a relationship between an amplitude of an arm swinging action and a sampling period of positioning data. A sine wave shown in FIG. 6 indicates an amplitude of an arm swinging action while time has passed. The GPS receiver always may acquire positioning data on this sine wave. In FIG. 6, assuming now that the period of this sine wave (namely, arm swinging period) is "T0", when the sampling operation of the positioning data of the GPS receiver is carried out in a period "T1" equal to the above-explained period "T0", travel speeds calculated in accordance with this sampling operation indicate instantaneous speeds at continuously fixed positions (a1, a2, a3, - - - , a5) on the trail of the arm swinging action. As a result, an average speed calculated from all of these travel speeds does not have a meaningful value. In other words, in this case, the travel speeds given to the user contain the large adverse influences caused by the arm swinging action, but do not indicate the travel speeds caused by the true motion.
Also, even when the sampling period is different from the arm swinging period "T0", if this sampling period is very approximate to the same period such as a period "T2", lengthy time is required in order to acquire the positional change in the arm swinging amplitude for 1 period as indicated in positions bl, b2, b3, - - - , b5 of FIG. 6. That is, lengthy measuring time is required so as to acquire the averaging effect. This implies that lengthy time is required until the travel speeds caused by the true motion are provided with the user.